Grid influence issues in the methodology of numerical modelling of non-stationary combustion processes

Abstract

Estimation of reserves of combustion process stability in gas turbine engine (GTE CC) based on artificial modeling of non-stationary process (NP) excitation in the combustion chambers in temperature-pressure parameters is an actual problem in engine engineering. An increasing number of aircraft require the use of engines with high gas dynamic stability (GDS) up to 30% and more, for example, when creating power plants for vertical and short take-off and landing aircrafts, ekranoplans (ground-effect vehicles) and etc. The use of computational fluid dynamics (CFD) tools for calculating combustion flows in the combustion chamber of a gas turbine engine is currently an integral part of the design process, since a numerical study, in contrast to a full-scale experiment, requires significantly fewer material resources providing the ability to model expensive and unsafe cases of aircraft flight operation that are difficult to implement at the stage of bench tests, such as: crossing a jet distrail or a shock wave front (e.g., when an ammunition detonates) in front of the air intake of an air-jet engine, critical crosswind during takeoff leading to flow separation on the air intake cowl, vertical gusts and atmospheric turbulence, flight at high angles of attack, aircraft evolution (slip, etc.). The results of numerical simulation are decisively determined by the limitations of the applied models and simplifying assumptions for the simulated flow. There are many sources of errors in any calculation using computational gas dynamics methods: accumulated calculation errors, sensitivity to grid size, discretisation, flow extrapolation in grid interfaces of the used solver (ANSYS.Fluent), errors of turbulence models, assumptions and simplifications applied to the design, etc. This paper considers the grid effect on the problem of proving the random nature of gas oscillations in the combustion chamber of a gas turbine engine, which is essential for determining the gas dynamic stability of the engine as a whole.